Fluid Intake During Exercise in Tropical Climate in Young Athletes with Pre-Exercise Euhydration or Hypohydration

Abstract

Many young athletes start exercise in a state of body fluid deficit, which magnifies the risk of an excessive increase in body temperature and may lead to deterioration of skills related to sports performance. It is not clear if when water is readily available their voluntary fluid intake during exercise compensates for the pre-exercise fluid deficit, or if it is not enough and initial hydration status worsens. PURPOSE: To compare the amount of fluid replaced during exercise in the heat between young athletes who arrive to an exercise session in a state of euhydration (EUH) and hypohydration (HYP) and are provided water to drink ad libitum. METHODS: Young athletes (N = 56, mean age = 15.7 ± 1.4 yr) completed an exercise sweat test, running or racewalking at an intensity > 70% of age-predicted maximum heart rate, in a hot and humid environment (WBGT = 28.5 ± 1.9°C). Pre-exercise urine specific gravity (USG) was used to categorize the athletes as EUH (USG ≤ 1.020 g/mL, N = 15) and HYP (USG > 1.020 g/mL, N = 41). Water was provided in bottles and they drank ad libitum. Sweat loss was calculated from the change in body weight [BW] (corrected for urine output) plus fluid intake. Dehydration was calculated as % change in BW. Ratings of perception of thirst (N= 35) and hot/overheated (N= 39) were examined with a 0 - 10 scale. RESULTS: Pre-exercise USG was higher in HYP (1.025 ± 0.003 g/mL) compared to EUH (1.013 ± 0.006 g/mL), P < 0.05. Exercise duration, sweat loss (27.4 ± 11.2 vs 24.2 ± 9.3 mL/kg) and urine loss (1.5 ± 1.6 vs 0.7 ± 0.4 mL/kg) were similar for EUH and HYP, respectively, P > 0.05. Despite fluid availability, fluid intake was low (EUH = 7.8 ± 6.3 mL/kg; HYP = 9.2 ± 7.5 mL/kg) and both groups showed significant reductions in BW (EUH = 2.0 ± 1.0%; HYP = 1.6 ± 0.8%), P > 0.05. Thirst increased during the session in both groups and was moderately high at the end (EUH pre = 2.2, post = 5.9; HYP pre = 1.9, post = 6.7). Mean perception of hot/overheated was high at the end of exercise (EUH = 6.3; HYP =7.2). CONCLUSION: Young athletes that start exercise in a state of hypohydration do not drink enough water during exercise to compensate for the pre-exercise fluid deficit and subsequent fluid loss, and their initial hydration status worsens. Thirst may not be a good indicator of the need to drink and the ad libitum intake of water is insufficient even when it is readily available.